The reliability of integrated circuits, discrete devices, connectors, printed wiring boards, backplane wiring systems, etc. is strongly influenced by theft environment. The harmful effects of moisture and contamination on electronic devices and assemblies are well documented. See R. B. Comizzoli, et al., "Corrosion of Electronic Materials and Devices" Science, Vol. 234, pg. 340-345 (1986). Contamination may be introduced during manufacturing, or it may be deposited from the ambient environment during use. Of concern is a 10-100 fold increase in the deposition rate of fine particles on critical component surfaces due to forced-air cooling, necessitated by the greater power densities found in many present-day devices and assemblies.
Atmospheric particles of concern typically exhibit a bimodal mass distribution over the size range of approximately 0.01-15 .mu.m in diameter. Particles larger than 15 .mu.m are usually removed by filtration systems. Coarse particles (about 1-15 82 m), which are likely to be rich in calcium and are derived principally from mechanical processes, are typically removed with approximately 95% efficiency by standard air filtration systems. However, line particles (about 0.05-1 .mu.m), which are likely to be rich in ammonium sulfate and other corrosive substances derived from fossil fuel combustion and natural processes, are difficult to remove by filtration and constitute the bulk of particles transferred indoors from the outdoor environment.
Fine particles are a significant corrosion hazard to most electronic devices because of their great ionic content. These particles tend to adsorb moisture from the environment, thereby forming an electrolyte. In the presence of an applied potential, leakage currents are set up and fault-producing electrolytic corrosion takes place. Ionic contamination of electronic devices, subassemblies and assemblies (collectively "components") from fine particles is an increasing cause of equipment failures.
While numerous chambers exist for life testing of electronic components and devices in the presence of gaseous contaminants, only a few have been described for testing with dust particles. See, EIA Standard RS-364-50, "Test Procedure #50 Sand Dust Test Procedure for Electrical Connectors," Electrical Industries Association, Washington, D.C., 1983. The few existing dust exposure chambers are designed to evaluate the effects of coarse particles (typically greater than 1 .mu.m). The air flow in prior art chambers is typically either turbulent or undefined, particle dispersion typically is accomplished by mechanical injection into a high velocity air stream, and particle concentration and deposition rate vary widely across the chamber volume. In view of the increased incidence of failures caused by fine ionic particles (typically &lt;1 .mu.m), means for realistically testing electronic components with regard to their ability to perform in a particle-laden atmosphere are needed for assessing and ensuring the reliability of, e.g., new circuit boards, connectors, hybrid integrated circuits, multichip modules, and the cabinets that house these components. Such means am described in this application.